1. Field of the Invention
The present invention is directed to a fluid friction clutch having a working chamber, a reservoir and a rotor in the reservoir and toward a method of distributing fluid in the reservoir, and, more specifically, toward a fluid friction clutch having a working chamber, a reservoir and a rotor in the reservoir, the rotor having a plurality of arms separated by gaps for distributing fluid in the reservoir and toward a method of distributing fluid in the reservoir using the rotor.
2. Description of the Background Art
Conventional fluid friction clutches include a housing having a working chamber, a reservoir and a valve for controlling the movement of a working fluid between the reservoir and the working chamber. A driven disk is mounted for rotation in the working chamber, and a degree of coupling between the driven disk and the housing is determined by the amount of working fluid in the working chamber. When substantially all the working fluid is in the reservoir, the clutch is disengaged, and the housing of the clutch is coupled to the driven disk only via bearing friction between the clutch housing and a drive shaft and friction produced by air located in the working chamber between the clutch housing and the driven disk. Releasing working fluid into the working chamber couples the motion of the driven disk to the housing. The rotation of the driven disc helps to transfer fluid from the reservoir to the working chamber, and if additional fluid from the reservoir is not provided to the working chamber, the coupling between the driven disk and the housing decreases. Such clutches may be used, for example, for driving a fan in a liquid-cooled internal combustion engine to help control the temperature of a circulating cooling medium.
When the temperature of the cooling medium is low, the working fluid is retained in the reservoir and there is little coupling between the driven disk and the housing. As the temperature of the cooling medium increases, an opening between the reservoir and the working chamber is uncovered. The rotation of the housing produced by the limited coupling between the driven disk and the housing draws fluid in the reservoir toward the opening and into the working chamber. The presence of the liquid in the working chamber increases the coupling between the driven disk and the housing and increases the rotational speed of the housing and this drives fluid from the reservoir into the working chamber at a greater rate, further increasing the coupling between the driven disk and the housing.
It will thus be appreciated that when the housing is rotating slowly, fluid is slow to move from the reservoir to the working chamber. When the housing is connected to a fan, this can delay fan actuation and possibly lead to an overheating of the engine or component cooled by the fan.
One conventional method of speeding the movement of working fluid from the reservoir to the working chamber is to provide a supplemental disk in the reservoir that is driven by the shaft that drives the driven disk. This concept is disclosed in U.S. Pat. No. 4,405,039 to Hauser which is incorporated herein by reference. The supplemental disk is mounted in close proximity to a wall of the housing in the reservoir to increase coupling between the drive shaft and the housing even when little or no working fluid is present in the working chamber. The rotation of the supplemental disk in the reservoir and the close spacing of the supplemental disk and a wall of the housing entrains the fluid to draw it toward the opening, and also tends to heat the fluid in the reservoir thus decreasing its viscosity and promoting more rapid flow. This approach provides benefits, especially at startup. However, the continual shearing of the fluid between the supplemental disk and the housing speeds the degradation of the fluid and also increases the load on the engine driving the driven disk. It would therefore be desirable to provide a fluid friction clutch that enhances fluid movement from a clutch reservoir to a clutch working chamber, especially at low speeds, which clutch produces less sheering of the fluid in the reservoir and less drag on the motor driving a driven disk of the clutch.